The present invention relates to a write circuit and a magnetic storage device using the same and, particularly, to a write circuit for use in a magnetic storage device such as a flexible disc drive device (FDD) or a hard disc drive device (HDD) which is capable of being written at different recording densities.
Although a current FDD, which is an external memory, usually can store information at a density of about 1 M bytes per magnetic recording medium, an FDD capable of being written at a density of about 2 M byte or about 4 M bytes per magnetic recording medium has been developed and is commercially available. The disc drive device capable of recording at about 1 M byte per medium will be referred to as a "1 mega byte device" and that capable of recording at about 4 M bytes per medium will be referred to as a "4 mega byte device", hereinafter.
FIG. 5 shows a conventional write/read circuit for a 4 mega byte device storing information at a density of about 4 M bytes per recording medium and FIG. 6 shows signal waveforms at various portions thereof for explaining a circuit operation. In FIG. 6, the waveforms are identified with letters that also used for circuit portions in FIG. 5 to clarify correspondence therebetween.
In FIG. 5, a write circuit 20 is constituted with a flip-flop 21, drivers 22 and 23 and a coil 24 of a read/write magnetic head, all of which are connected in the described sequence. A read circuit 30 is constituted with the coil 24 of the magnetic head, an amplifier 25, a filter circuit 26, a differentiator 27, a zero volt comparator 28 and a pulse shaper circuit 29, all of which are connected in the described sequence.
In the write circuit 20, a write signal A (see waveform A in FIG. 6) which is a pulse signal containing data bits or a combination of clock and data bits is supplied to a trigger input T of the flip-flop 21. The flip-flop 21 changes its state upon every reception of the write signal A. A signal B which is a Q output of the flip-flop 21 is thus changed in its state in accordance timing of the signal A (see waveform B in FIG. 6). The driver 22 produces a write current in one of a supplying or sinking direction in synchronism with the state of the signal B. The driver 23 is responsive to a Q output of the flip-flop 21 to produce a current whose direction is opposite to the direction of the write current C.
As a result, the write current C whose direction is switched according to the write signal A, flows through the coil 24 (see waveform C in FIG. 6), upon which a magnetic medium (not shown) is magnetized in a direction determined by the direction of the write current C through a magnetic head (not shown) on which the coil 24 is wound (see magnetizing waveform D in FIG. 6).
In this case, the flip-flop 21 serves as a binary signals generator for generating binary signal "1" and "0" corresponding to the write signal A, as shown by the waveform B in FIG. 6.
The read circuit 30 detects the magnetized state of the magnetic medium to which data are written by the write circuit 20 an electro-motive force generated in the coil 24 of the magnetic head. The electro-motive force detected is amplified by the amplifier 25 and supplied to the filter circuit 26 as a read signal to obtain a read signal E corresponding to a changing rate of magnetization D (see waveform E in FIG. 6). The signal E is differentiated by the differentiator 27. A resultant signal F crosses zero points at extremes of the signal E (see waveform F in FIG. 6). Then, the signal F is binarized by the zero volt comparator 28 according to positive and negative values of its waveform. As a result, a signal G which is inverted at every extreme of the magnetization D is obtained (see waveform G in FIG. 6). The pulse shaper circuit 29 produces pulses when the signal G inverts. Thus, the write signal A is reproduced as a read signal H (see waveform H in FIG. 6). The reason why the read signal H is the reproduction of the write signal A is that the direction of magnetization D is quickly changed at each reception of a write signal pulse A and the timing is detected as extremes of the magnetization D.
The above discussion applies, in principle, to FDDs regardless of their information recording density, whether 1 M byte per medium or 4 M byte per medium. However, since the recording density of the 4 mega byte device is 4 times that of the 1 mega byte device, a magnetic head and an associated coil 24 thereof are required to be electrically operable a correspondingly higher speed. Further, in order to make the 4 mega byte device compatible with the 1 mega byte device, the 4 mega byte device is made operable to read data written on a medium by the 1 mega byte device. To this end, the filter circuit 26 has a plurality of different filtering characteristics for the 1 mega byte device, a 2 mega byte device and the 4 mega byte device, which can be switched by a selection signal K, so that the 4 mega byte device can read information recorded on the medium by any of the FDDs.
The selection signal K is usually generated by detecting identification holes formed in each medium by means of the detection circuit 10.
Thus, the 4 mega byte device can have the highest level compatibility with other devices. However, a lower level compatibility of it is not always provided. That is, the 4 mega byte device can not always record information on a medium to be used in the 1 mega byte device for reading by the 1 mega byte device. This is because the 1 mega byte device which had been developed earlier and has been used widely does not have any means for providing compatibility with the 4 mega byte device which was developed later.
When a 4 mega byte device writes data on a certain medium recording density corresponding to a 1 mega byte device and the data are read by the 1 mega byte device, there is a problem which will be described with reference to FIG. 3.
Waveforms A, B and C in FIG. 3, which are obtained when the above mentioned writing of data is performed by using the circuit shown in FIG. 5, are the same as those shown in FIG. 6 except that the frequency of inversion becomes lower. However, due to the lower inversion frequency, the magnetization waveform D becomes wider as shown in FIG. 3.
Due to the wider magnetization waveform D, the inversion of magnetization becomes very sharp when data are read by the 1 mega byte device as shown by waveform E in FIG. 3. This is mainly due to a difference in characteristics of a magnetic head between the 1 mega byte device and the 4 mega byte device.
There is no such sharp inversion of magnetization when data writing is performed by a magnetic head used in an existing 1 mega byte device. When such a signal as waveform E shown in FIG. 3 is generated as a read signal in the 1 mega byte device and differentiated therein, a resultant signal F is nearly zero volts in areas Fa and Fb in which magnetization D is stable. Therefore, a signal G from the zero volt comparator 28 includes noise in these areas, causing a normal read to be impossible.
The relation between the 1 mega byte device and other devices having lower recording densities is different from the relation between the 4 mega byte device and the 1 mega byte device and the recording capacity is increased mainly by increasing the number of tracks. The compatibility therebetween is mainly in a format of medium and has substantially no such problem as mentioned above.
The waveforms in FIG. 3 are more or less exaggarated to clarify the relation between the 1 mega byte device and the 4 mega byte device. In a case where data recorded by the 4 mega byte device at a recording density corresponding to that of a 1 mega byte device are read by the 1 mega byte device, the data may be correctly read by retry or error detection such as a CRC check if the waveform of the data has a light pulse form as compared with the waveform E in FIG. 3. However, this does not guarantee that data which are recorded at a recording density corresponding to the 1 mega byte device by the 4 mega byte device are read by the 1 mega byte device.